Re: [PATCH v14 03/10] accel: collecting TB execution count

[Wu, Fei]

On 6/1/2023 8:05 AM, Richard Henderson wrote:
> On 5/30/23 01:35, Fei Wu wrote:
>> From: "Vanderson M. do Rosario" <vandersonmr2@gmail.com>
>>
>> If a TB has a TBS (TBStatistics) with the TB_EXEC_STATS
>> enabled, then we instrument the start code of this TB
>> to atomically count the number of times it is executed.
>> We count both the number of "normal" executions and atomic
>> executions of a TB.
>>
>> The execution count of the TB is stored in its respective
>> TBS.
>>
>> All TBStatistics are created by default with the flags from
>> default_tbstats_flag.
>>
>> [Richard Henderson created the inline gen_tb_exec_count]
>>
>> Signed-off-by: Vanderson M. do Rosario <vandersonmr2@gmail.com>
>> Message-Id: <20190829173437.5926-3-vandersonmr2@gmail.com>
>> [AJB: Fix author]
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> Signed-off-by: Fei Wu <fei2.wu@intel.com>
>> ---
>>   accel/tcg/cpu-exec.c          |  6 ++++++
>>   accel/tcg/tb-stats.c          |  6 ++++++
>>   accel/tcg/tcg-runtime.c       |  1 +
>>   accel/tcg/translate-all.c     |  7 +++++--
>>   accel/tcg/translator.c        | 25 +++++++++++++++++++++++++
>>   include/exec/gen-icount.h     |  1 +
>>   include/exec/tb-stats-flags.h |  5 +++++
>>   include/exec/tb-stats.h       | 13 +++++++++++++
>>   8 files changed, 62 insertions(+), 2 deletions(-)
>>
>> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
>> index 0e741960da..c0d8f26237 100644
>> --- a/accel/tcg/cpu-exec.c
>> +++ b/accel/tcg/cpu-exec.c
>> @@ -25,6 +25,7 @@
>>   #include "trace.h"
>>   #include "disas/disas.h"
>>   #include "exec/exec-all.h"
>> +#include "exec/tb-stats.h"
>>   #include "tcg/tcg.h"
>>   #include "qemu/atomic.h"
>>   #include "qemu/rcu.h"
>> @@ -562,7 +563,12 @@ void cpu_exec_step_atomic(CPUState *cpu)
>>               mmap_unlock();
>>           }
>>   +        if (tb_stats_enabled(tb, TB_EXEC_STATS)) {
>> +            tb->tb_stats->executions.atomic++;
>> +        }
>> +
>>           cpu_exec_enter(cpu);
>> +
>>           /* execute the generated code */
>>           trace_exec_tb(tb, pc);
>>           cpu_tb_exec(cpu, tb, &tb_exit);
>> diff --git a/accel/tcg/tb-stats.c b/accel/tcg/tb-stats.c
>> index f988bd8a31..143a52ef5c 100644
>> --- a/accel/tcg/tb-stats.c
>> +++ b/accel/tcg/tb-stats.c
>> @@ -22,6 +22,7 @@ enum TBStatsStatus {
>>   };
>>     static enum TBStatsStatus tcg_collect_tb_stats;
>> +static uint32_t default_tbstats_flag;
>>     void init_tb_stats_htable(void)
>>   {
>> @@ -56,3 +57,8 @@ bool tb_stats_collection_paused(void)
>>   {
>>       return tcg_collect_tb_stats == TB_STATS_PAUSED;
>>   }
>> +
>> +uint32_t get_default_tbstats_flag(void)
>> +{
>> +    return default_tbstats_flag;
>> +}
> 
> What is the purpose of this function, instead of a global variable?
> What is the meaning of 'default' in its name?
> 
tbs have their specific settings, e.g. after 'filter' cmd:
* the last_search tbs has their stats_enabled kept
* tbs not in the list sets their flag to TB_PAUSED

I guess 'default' means the flag for creating new tbstats.

>> @@ -295,6 +295,7 @@ static TBStatistics *tb_get_stats(tb_page_addr_t
>> phys_pc, target_ulong pc,
>>       new_stats->pc = pc;
>>       new_stats->cs_base = cs_base;
>>       new_stats->flags = flags;
>> +    new_stats->stats_enabled = get_default_tbstats_flag();
> 
> Is this merely to record how we have generated a given TB?
> What is the purpose of this flag over the global variable?
> 
see above.

>> diff --git a/include/exec/tb-stats-flags.h
>> b/include/exec/tb-stats-flags.h
>> index 87ee3d902e..fa71eb6f0c 100644
>> --- a/include/exec/tb-stats-flags.h
>> +++ b/include/exec/tb-stats-flags.h
>> @@ -11,6 +11,9 @@
>>   #ifndef TB_STATS_FLAGS
>>   #define TB_STATS_FLAGS
>>   +#define TB_NOTHING    (1 << 0)
>> +#define TB_EXEC_STATS (1 << 1)
> 
> Why is NOTHING a non-zero flag?
> 
yes, it might looks better. But there is no correctness issue either as
it checks if the specific bit is enabled during collecting stats.

>> --- a/include/exec/tb-stats.h
>> +++ b/include/exec/tb-stats.h
>> @@ -31,6 +31,9 @@
>>   #include "exec/tb-stats-flags.h"
>>   #include "tcg/tcg.h"
>>   +#define tb_stats_enabled(tb, JIT_STATS) \
>> +    (tb && tb->tb_stats && (tb->tb_stats->stats_enabled & JIT_STATS))
> 
> Inline function, though again, why stats_enabled vs global variable?
> 
will inline it.

Thanks,
Fei.

> 
> r~